stonewort; Chara braunii
A genus of green algae found in fresh water. Often refers specifically to Braun's stonewort (Chara braunii).
A lot of stonewort is growing in the pond.
charophyte
Katakana spelling is standard for this organism name.
Kanji spelling is rare; the word is usually written in kana.
From 車軸 (shajiku, 'axle') + 藻 (mo, 'algae'), referring to the whorled branches resembling an axle. The exact derivation is uncertain.